Propeller and method of propeller manufacture



July 24, 1951 E, R, LOCHMAN l 2,561,705

PROPELLER AND METHODS OF PROPELLER MANUFACTURE Filed Aug. 8, 1942 lENTORJuly 24, 1951 E. R. LocHMAN PRPELLER AND METHODS OF' PROPELLERMANUFACTURE 5 Sheets-Sheet 2 Filed Aug. 8., 194?,

July 24, 1951 E. R. LOCHMAN 2,561,705 PROPELLER AND METHODS OF PROPELLERMANUFCTURE Filed Aug. a, 1942 3 Sheets-Sheet 5 15.9 1 INVENTOR. 1 A mA519.16.

T TORNEYS.

sembIY,

Patented July 24, 1951 PROPELLER AND METHOD OF PROPELLER MANUFACTUREEmil R. Lochman, Milwaukee, Wis. Application August 8, 1942, Serial No.454,146 i 7 Claims.

This invention relates to propellers and methods of propellermanufacture, and more particularly to a controllable pitch propeller forvarying and controlling the pitch of the propeller in accordance withthe operating conditions.

The principal object of this invention is to provide a simplifiedconstruction of a controllable pitch propeller, adapted for massproduction, and .adapted to be used and mounted on the engine shafts ofthe present day airplane engines, for immediate production.

A further object of the present invention is to reduce the number ofoperating parts, to avoid parts requiring very costly machiningoperations.

While any type of blade may be used in the feathering hub constructiondisclosed herein, it is a further object of this invention to improvepropeller construction by strong internal reenforcements of -a hollowblade and by changing the shape of the blade to avoid extreme formingstrains and byproviding a method of forming the blade in two halvesandleaving a hollow passage `from the root to the tip of the blade in theform of a combination spar for the purpose of aiding in the constructionof the blade as well as increasing its strength, rigidity and thrustcapacity.

Further objects of the invention will appear in the followingdisclosure. `The means by which the objects of the invention areobtained are more fully described with reference to the drawings, inwhich:

Figure 1 is a top plan view of the propeller aswith parts broken away toshow part of the hub section and other operating parts in cross section,as well as showing the nose section of the airplane engine and themanner in which the .propeller is attachedthereto.

Figure 2 is arear elevation of the propeller assembly,` with parts cutaway showing a cross section of the operating parts on line 2-2 ofFigure1, but omitting the nosesection of the airplane engine, while thepropeller hub has parts broken away to show a part incross section.

Figure 3 is a fragmentary view of a single blade assemblyin itsrespective hub socket, showing in radial section the respectiveoperating parts and certain welding joints, a part of the bladeappearing in elevation.`

Figure 4'fis a` side view of the essential parts of a welding .deviceshowing two halves of a propeller in cross section as prepared forresistance welding.` according to the process herein disclosed.

`Figure 5 isa side View of a jig showing the cross section of. apropeller prepared for brazilie ina brazing furnace.

Figure 6 is a fragmentary cross sectional View of a hub assembly on lineli-B of Figure 3, showing the rack and pinion control of a propellerblade.

Figure 7 is a front elevation of a propeller blade showing the essentialparts of the construction, including the core shaft and the connectinginternal spar.

Figure 8 is a plan view of the blank for forming a half section of apropeller blade.

Figure 9 is a `perspective cross sectional view of propeller sectionsshowing the internal spar in half section as prepared for resistancewelding the half blades shown in Figure 4.

Figure 10 is a plan view of a core die for forming the spar with asurface for attachingthe blade sections according and conforming to thepitch of the blade.

Figure 10a is a fragmentaryelevation of the bottom section of the coreshaft showing the spar and a half section of the blade attached thereto.

Figure 11 is a plan view of the spar blank, showing welding slots.

Figure 12 is a cross section of a half spar prepared from a half sectionof said spar blank for use as shown in Figure 9. l

Figure 13 is a plan view of the bottom section of the core shaft showingthe bottom section lof the spar Welded thereto.

Figure 14 is a fragmentary cross section of the root of the bladeshowing the relative parts of the core shaft, spar and blade sectionwelded and brazed together.

Figure 15. is a fragmentary cross sectional view of the same parts asarranged for resistance weldmg.

Figure 16 is a cross section on line lli- I6 of Figure 13, with partsbroken away showing the position for the end llers, welded in place itoclose and nish the bottom of the blade, also showing spot welding forrigidly connecting the spar to the blade. i

It will of course be understood that the description and drawings aremerely illustrative of the present preferred form of application,` andthat various changes and modifications may be made in the structuredisclosed without departing from the spirit of the invention, especiallyin tting it to various types of airplanes and :for their varyingrequirements and services.

Several of the features of my invention are usable independently of eachother and in various combinations, being separately described andclaimed. I shall hereinafter summarize these features and theirproperties.

For assistance in analyzing my disclosure, I may state that the completeapparatus hereinafter to be described includes:

1. A variable pitch propeller having important features of hub design,irrespective of the particular blades used therein.

2. A novel and improved propeller blade structure andprocessofmanufacture which .is vparticularly adapted for a variable pitchpropeller, but

may be used in any propeller of variable pitch or otherwise, andirrespective of the particular hub or pitch varying mechanism.

Reference will first be rnade'fto Figures 1 and 2, where I haveillustrated the:

Propeller assembZy.-The propel-ler .assembly comprises a hub 15 mounteduponV and driven by a propeller shaft 10, which,4 in some installations,may also comprise the enginershaft, .but which, in the device asillustrated, is driven at av reduced speed from the engine shaft 18'l"through conventional reducing gearing (not specically illustrated),housed in the casing `which is' shown in plan 1n Figure 1 surroundingthe engine shaft and the propeller shaft 18.

`The propeller shaft projects, in a conventional installation, from thenose housing member 1| ofthe plane, such member being bowl-shaped. On`the `projectingportion of the propeller shaft,

` which, in'accordance with conventional practice,

.is splined, -`the hu'b 15 having complementary splines 18'., is.mounted yand positioned between taper collars 11 and 18 which are drawnsnugly into the hub by theA nut 19 securedto the end u :of the propellershaft.

'The taper collar 11 is engaged by the tubular lrearward, extension 16ofthe hubV proper, along which the `actuating disk for featheringtheblades of the propeller is slidably movableas will hereinafter beexplained. y,

The one-piece plain hub of suitable steel has three radial blade sockets|05 with plain "bores |08 for controllablymounting the 'three vpropeller.blades B346, B341 and B3{38.` 4.blade has a vhollow core .shaft |62(see Figure 3) Each with a finished root section`j|6| on which 1 ,mountin series the nut, |||v withdts locknut [1| |2.; -a'set of .felt washers||j4 .which are pressed into the recess of nut j`|:|| Aforming' a greaseseal; a set of radial ball bearings Alllll with `their Aouter racesseparated byjwashers, 4`a heavyT thrust bearing llll; an additional setof radial lball bearings |81 separated attheireinner races b y washers|24 v(thereby,transferring the very .severe end vthrust to the raisedsection |01vof i said pinion 95) and, finally, a pinion 95.

The vseveral parts described as4 mounted `in .series on the root section|6| of the propeller `core shaft areheld thereon by'thenutl E screwed y.to the .inner end of the core shaft.

The core shaft, 'in turn,` together with all of the parts abovedescribed, is then finally anchored to the blade socket |05 of the hub15 bythe nut fandlock nut 2. e In lieu, of a key 'for positively fixingthe several propeller core shafts to their respective pinions v toassure operation in exact unison, I may use pins which projectaxiallyfrom the core `shaft. shoulder |114', as shown in Figures 1, 10a

and 6. The pin H5, is primarily relied upon to Alocate the parts, whilepinsl ||4 provide sup- ,plemental torque transmitting strength.

AThe teeth 96l of the pinion .85 and the teeth ofthe racks 8| .must beset in precisely the same position lfor all three blades, andthisposition is permanently held by the set-pin ||5, so

`the "racksl, which reciprocate iin thengbores 8l' and are connectedwith the pressure disk 88 e by upsetting their reduced ends against theinner surface of the pressure disk about the holes in the pressure diskthrough which the reduced ends of the racks 8| extend (Figure 6).

At their forward ends |22 theracks 8| are connected 'for unitarymovement by an annular plate 82 .having 'apertures to receive thereduced and. threaded forward ends of the racks 8|. Nuts T23 securelyclamp the.. annular plate 82 to the respective racks. The annular platemay be guided for sliding vmovementA `along 'the propeller nut 19` towhich its central opening 83 maybe tted- (Figurel and Figure 6).,` Asthe'annular plate 82 moves outwardly along the propeller nut 19 it willencounter the pressure cap 84 which is urged rearwardly `upon the nut bya powerful compression spring 86 seated in 'the nose cap 81 bolted tothe hub.' This spring aids in resisting thrust ofthe propeller blades'in their extreme featheringfposition, and consequently assists inreturningtheblades `from 'such extreme feathering position. ""Ihefour-holes 19' provided in the propeller nut-are to-facilitate the useof a lever for tightening-the nut on its shaft,

whereby 'to position the propeller vhub 'snugly between the tapercollars 11"and 18 jwhich assure correct `tracking ofthe blades.'

' Transmission casing T `i'sWshownV in 'Figurer' 1 as attached to vthenose section 1| of present day engines so that the propellers can beused for badly needed war production -without delay,

or vwaste of timefor changes of present day equipment. The particulardesign of thev parts shown to illustrate vtheapplication of 'theinvention would `obviouslyr be quite different but for the desirabilityof `making `'these parts adaptable to ,existing engine nose sections.

Figure 2 is shown without said nosesection 1|, and it is of course selfevident that said nose section can readily be built toaccommoda'te-thecomparative simple transmission parts for op- ."erating this newcontrollable pitch propeller, as the few engine parts housed in 'saidpresent day nose section readily't myltransmission parts vas plainlylshown in Figure 1.`

An important feature of my invention from a military standpoint lies :inthe fact that the very important and lvulnerable electrical operatingparts have been removed 4from the much exposed nose section,wherepreviously known electrically operated propellers have hadv suchparts. According Ato my invention, these parts are, nowk placed in thecockpit where they ,are now under the constant' observation of theaviator and a hand control is provided so that under lightingvconditionswhere any of the control parts may be destroyed the aviatorcan .keep flying by using the hand control and this enables him to makea'safe landing.

` My improved transmission T comprises a band 13 applicable by means ofscrews '14 to the existing nose section 1| of the plane. Asbest shown inFigure 2, this casing provides 'bearings at B9 `and |08 forthe upperandlower shafts 94 which are connected by a gear train comprisingintermediate gears 35 and gears `fnd it convenient to provide thepecially in the root section thereof. fous features of the blade andmanufacture are shown in Figures 3 to 16, in- 75 |36, which arerespectively mounted upon the shafts 94 so that such shafts turn inunison.

Each of the shafts 94 carries two pinions 93,

Athe several pinions being properly located to 5 `mesh with four racks92 connected to the non- Vrotative outer race 90 of a compositeanti-friction bearing set through which motion is transmitted to thepressure disk 80 for actuating the blade feathering racks 8|.

rocation by the rods |03 and |03' (Figure 1).

Because of the high speed rotation involved, I

anti-friction connection between the outerl race 90 pressure plate 80 bymeans of rollers |26, each of which is provided with its ownanti-friction bearing mounting upon the pressureplate 80.

It will vbe apparent that by the arrangement described any rotation ofshafts 94 is immediate- 20 ly translated by means of the pinions 93 andthe racks 92 into an axial movement of the outer Vrace 90, municatedthrough the bearing structure |26 to the pressure plate 80 and thence,by means of 25 such axial movement being cornracks 8| and pinions 95,again translated into feathering rotation of the respective blades upontheir respective axes. The mechanism described is extremely sturdy,simple, and effective, and

the disposition of the cross shafts 94 is such that 30 y they may betted around the existing nose section of present day airplanes withoutinterference with any of the existing structure.

The only requirement is that transverse openings be bored into theexisting nose casings 1| to receive 35| f these shafts and theirbearings.

So sturdy a mechanism requires no protection but it may be enclosed forstreamlining purposes and for dirt exclusion by a housing |60 (Figure 1)40 The power for operating the actuating connections thus far describedmay be derived in a variety of ways. But I have chosen, for illustrativepurposes, to show the power communicated to this mechanism by means ofanother "45 rack |4| which extends from the pilots compartment to meshwith a pinion |35 on a shaft |39 connected to one of the gears |35 inthe gear train, which provides connection between shafts` 94 (seeFigures 1 and 2). l

Thus, in my preferred organization, there are three stages oftransmission, each involving rack and pinion. In the first thereciprocating motion of the rack |4|, engaging pinion |35 is used torotate shaft |39. pinion stage, the rotation of the shafts 94 (gearconnected with shaft |39) is used to reciprocate the` racks 92. Thismotion, communicated through the outer race 90 of the anti-friction#y,bearings |26 to the rotative pressure plate 80, 60

to meet the needs of a sturdy pitch adjusting 65 propeller with powerand size adequate to Serve large military and transport planes. Thestructure and its method of construction are adapted considerably toincrease the rigidity and strength of the blades with particularreference to their `70 ability to withstand combined torsional andcentrigual strains throughout the blades, but es,- 'rhe `varits A,method., of

I taper |62 The non-rotatable 10 *louter race 90 is further guided inits axial recipand the 4shown in dotted unes 204, 204.

In the second rack an`d""55 elusive, in addition to the partialdisclosure in Figures 1 and '2;

Figure 3 showsthe assembly of the root of the blade mounted in the bore|08 of the hub socket |05 as above described; the core shaft |61 has ato conform with the tapering form of the spar |10. continuation of theshaft, being mounted thereon by plug welding |15 (see Figures 4, 5 and13) through punched slots |14, |15 formed in the blank |16 of Figure 11.The core shaft IBI and spar |10 undergo several fabrication stagesbefore being finally incorporated into the propel- ,ler blade, As bestshown'inFig. 4 the preferred spar as shown in Figures 1|), 10a, 5 and13.' The core shaft and spar half sections `are firmly joined by weldsapplied to their mating edges at the same time as the blade halfsections are mated. As best shown in Fig. 15 the same weld |19 desirablyjoins both spar half sections and blade Vhalf sections. In addition tothis connection the projecting stub shaft of the core IBI has its twoparts united by the screw bolts |92. As best shown in Figs. 3, 7, and 9the core shaft |6| extends only partially into the propeller blade andterminates at weld |62. The spar |10, however, continues on for theentire length of the blade, dividing toward theV tip, as shown at |18,into spaced arcuate webs as the blade narrows. Figure l2 shows a halfspar formed from the half blank |11 and used in the process of joiningthe two half blades |194, |95 by arc welding as shown in Figure 4, wherethe two half blades are held firmly in mutually insulated oarriageclamps of an arc welding apparatus, each being especially prepared withcircular sections 20| and respectively blocks 203 tting thereto, andbeing adjustable in slots 2|1 for the purpose of accurately setting therespective blade sections, all being adjusted to the common axial center0 2|2, of which two are shown; namely sections `V and 5a.

The respective adjustment of the latter is For repetition work at thesame setting they bolt 201 is opened and theupper linked portion 2|| isswung open as shown by arrow `209 for taking out a welded propeller andinserting two other half blades without changing the respective sectionblocks 203, 203. For clearness of presentation only one clampingcarriage device is shown while another like clamping apparatus ismounted on the slide |98, being moved on the slide rails |91 mounted onthe bed |96 for the purpose of accurately holding the two half sectionsfor resistance welding, for which object the blade edges |19 aresomewhat extended so they can fuse during the application of the currenton wires 209, 2| 0.

The hollow spar has the further object of receiving the welding grit andthe provision of havingan open bore |63 in said core shaft andcontinuing from the root to the tip of the blade,

` is for the purpose of removing all loose grit after the are welding.Thereafter I insert a suitable vquick'hardening paste or coating of taror pitchlike substance for arresting remaining particles The sparpractically forms a `accessible surface f -zthereby anchoring :the grit-against displacement.

Furthermore, the hollow passage of the spar is then packed with suitablefelt or other 'packing |10 to fully arrest -any particle vfrom loosening'or moving under the centrifugal force of .the .running propeller, forthe purpose of permanently retaining absolute balance of it.

To facilitate application by arc Welding into the two Vhalf blades, the`core shaft |6| Ais also formed in halves and screw bolts |92 areprovided to properly locate said halves in the Welding apparatus .andfor clamping said halves permanently.

Figure 10 shows a `spar die |81 with respective fiat pitch line'surfaces` |90 as well as ,an enlarged cross section with a completespar formedaround said :die and showing the joint section |88 extends atthe root section and .centers |88 are applied at either .end .forproperly operating said vdie in a suitable machine. An .alternateprocedure vof securing the hollow blade 4form 221 to the spar shown inFigures 2, 3 and .16, .and in said proce- .dure the core shaft remainsin .one piece and the smaller bore |63 is .first bored .and then thelarger one .|63 Ais made, thereby leavingthe inner .shoulder |92',leaving the stock Vto receive the bolts |92.

The plug welding |14 may be done by .arc welding. The two half blades,as well as the bottom seal |6|' and the top seal |62 may be put on by4spot welding. .shown in Figure 5 has the same circular sections forsetting the respective blocks 2|.3, 2|9. However, they .are preferablyof brick or other .fire resisting .material as in this alternateprocedure the joining `of the half blades |94, |95 is.-

reenforced by brazing in a brazing furnace, and while it is known thatlattempts have been made .for filleting certain weldings by solderingwith ,soft cuprous metal, such usage would not perform the function ofuniting my two .half blades into a Asolid unit and to stand the strainon the joint.

The sectional setting of the half blades .in both procedures of weldingis alike as shown in the setting of sections 4b and 5b. Both of thoseshown, as well as the entire series required by the whole leng-th of theblade (see .Figure 7, sections a to h) .have the same axial center.2|.2, and .the .entire .series is permanently adjusted in the respectiveapparatus and after nish welding of one blade the setting is opened byloosening the bolt 201 and .the ,lock 2.|4.` Then, turning the lock out--ward i-n the direction of .arrow `2|5, the entire section 2| of theapparatus is turned open in the direction of arrow 208 `withoutdisturbing the setti-ng of the blocks 2|3, 2|-9, and the finished bladeis taken out and the next two half blades setr in. It will be notedthatl in this .apparatus the blade is on -edge and is supported at thebottom with the Wedges 'held in place by links 2|6., which supports areof course applied to ll sections in order to definitely set the .correctpitchv of the blade before welding.

It will, of course, be understood that the clamping apparatus shown .in.Figure 5 is duplicated at intervals throughout the length of the 'bladeso thatall .portions of the 4blade are rigidly .supported the properposition .before welding or` brazing are undertaken. y

later said bolts |92 arev used i |B| A chucking |10 is by spot weldingasf.;

The welding apparatusy 2|5 while the top half is fabricated,

'224 isset in place as root section. Said fillers are Aof distortionresulting Fig. 15.

labor and material.

v .When the-brazilie material in the for-m .of kwires shown in Figure,the; structure is suitably heated to brazing temperature for the purposeof permanently brazing `the `.two -half blades together, as shown inFigure 1-4, which especially shows the root section of the blade withthe fil-1ers v|69 in proper position to finish -said for the purpose :ofgiving the root section of the blade greater strength, to increase thethrust of this section, as well as to help in the cooling of the engine;a further great advantage is to reduce the strain on the sheet steel insuitably forming the blade (see Figure 8, showing the blank for a halfblade .and in dotted lines the section |83, |84 which will form theleading edge as well as the trailing edge for each respective blade).

As indicated in Figure 8, the blade blank is wide clear to its shankportion. This requires the use of fillers |69, but involves far lessdistortion `of the blank than would be required to reduce it to a smallroot diameter. Moreover, the broad .face of the blade continuing clearto its root is of great assistance in propulsion and in cooling theengine which drives the propeller. The lack from choice of the blankform indicated in Figure 8 makes it possible to extend the .blade to anydesired length, such .as would not be possible to achieve with moreconventionl blank contours.

This advantage is further increased by split curving the tip of theblade and forming .the camber face |82 so that in the folding process itwill strike the pressure face in Such a man- ,ner that suitable spotwelding |82 will nish the tip as shown in Figure 9. This View also showsthe folded sections |83' and |84' as perspective cross sections, whichalso show the shaping and suitable 4mounting of the vhalf spar |18 by.suitable Welds |18' in the preparation of the 'half blades for Weldingthem together as shown in Figure 15 shows the finished welded joint |19,as well as the fillers |69. See Fig. 16 for the welded finish |69', |6|,that view furthermore illustrates the strong root section of the coreshaft |6| With its bore |63.

In order to summarize the several features of the invention in thecomplete system illustrated, the following list of their advantages isbriefly stated:

The hub design presents important advantages in that it is of unusualstrength and of unusual simplicity. Unlike many variable pitch propellerstructures, the hub for the propeller herein disclosed is unitary, andis preferably not only unitary but made in one single piece, requiringonly the provision of the several bores and machined bearing surfacesherein described. It therefore has exceptional strength and offers aminimum of air resistance. .It is made with a minimum of AnyY number ofblades may be mounted without any fundamental change in hub design.

The propeller blade has a great many advantages in the Way ofsimplicity, economy of manufacture, lightness, strength and efficiency.The blade is unique in the manner of its internal reenforcement and theprovision of a shaft mounted in such reenforcement to project from theroot end of the blade for its mounting. It is also unique in thespecific manner in which it is being made of channel-shaped blade partseach comprising sheet metal folded upon a line representing the leadingor trailing edge of the blade so that the union between the parts isinade-v along the center camber faces. The blade is also unique in theconstruction of its tipV and its root portions. While particularlyadapted for use in a variable pitch propeller,l the blade is of such acharacter that it may` be mounted in any hub for use in any type ofpropeller, variable pitch or other- Wise, and its pitch adjustment maybe controlled in any manner.

The method of blade manufacture is closely related to blade structureand makes possible the specific features of Iblade construction above rited. The method involves the particular manner in which the componentparts of the blade a're pre-fabricated and joined together,including'not only the channel-shaped members which provide portions ofthe blade faces, but also the reenforcing or spar sections which areincorporated within the blade and serve to mount the stub shaft uponwhich the blade may be mounted in the hub. The preferred method of blademanufacture includes the construction of channelshaped core shaftblanks; the construction of channel-shaped spar elements concentric tothe channel-shaped core shaft blanks; the construction of channel-shapedleading and trailing blade elements each including pressure and camberface portions; the welding of the spar and core elements` to therespective portions of the blade elements, desirably using.pl"ug Vweldsat the root portion of the blade and marginal welds at the tip portionwhere they divideinto arcuate spaced webs; and the subsequent weldingmarginally of the corresponding edge portions of the blade elements andspar elements to unite the assembled blade, spar and core shaft elementsupon a plane transverse with respect to the blade between its leadingand trailingedge. In this manner the respective half sections of coreand spar rigidly support the blade half sections during the fusingprocess which joins both the blade sections and the core and spar alongtheir abutting midchords.

The method is also concerned with elimination of material unavoidablyleft by the welding or brazing operations in the interior of the blade.Such material must be either completely removed or completely xed as toposition, as otherwise it would, when dislodged, destroy the balance ofthe blade. The method of construction includes the removal of all suchmaterial as is loose, and the permanent fixation of the remainder, thepacking used as a part of the fixation process being variable as toamount, whereby to assist in balancing the blades against each l other.

I claim:

l. A fabricated propeller blade comprising a pair of channel-shapedelements respectively folded longitudinally to provide trailing andleading blade edges, each of said elements comprising camber andpressure faced blade sections, and each of said elements having itscamber face sections dished adjacent the tip of the blade whereby toclose at the blade tip the hollow interior of the blade, correspondingsections of the respective elements being marginally joined along linesextending longitudinally of the blade faces intermediate the leading andtrailing edge thereof, in further combination with centrally aperturedclosure means at the blade root fitted between the camber and pressureface sections of the respective elements.

2. In an airplane propeller, the combination with a hub having a tubularoutward extension line of the pressure and extension to constitute eachincludingjapropeller edge and contiguous portions of its pressure andcamber faces, folding the respective blanks along their respective edgeportions, whereby to constitute channel-shaped propellerelementsr'constructing opposing channel-shaped vsparmembers adapted tofit between the' opposing face" poi' tions of the respective blanks,welding said spar members marginally between the opposing face portionsof the respective channel-shaped blade elements to providereenforcementindividually therefor, and welding the respective blade nelementsmarginally along their corresponding pressure and camber face portionsintermediate their respective leading and trailing edge portions.v

4. Arnetliod of propeller blade manufacture which comprises theconstruction of a pair `of semi-tubular core shaft elements, theconstruction of a pair of spar elements having semi-tubular portionsconcentric to the respective core shaft elements andvhaving otherportions extending axially beyond said core shaft elements, the weldingof said spar element portions to the core shaft (elements,theconstructionl `of a pairgof channel-shaped blade elements, eachincludinga Jlade edge and contiguous pressure and camber face portions,welding of the spar elements marginally to the opposing face portions ofthe respective channel-shaped blade elements, and the subsequent weldingtogether marginally of corresponding face portions of the respectiveblade elements, whereby to provide an internally reenforced hollowblade.

5. A method of propeller blade manufacture which comprises theprefabrication of channelshaped blade and spar elements, welding thesaid elements together to constitute a reenforced blade in which thereenforcing element provides a passage throughout the interior length ofthe blade, dislodging through said passage loose material left from thewelding, together with the step of packing filling material into atleast a portion of said blade, whereby to immobilize therein materialloose but not discharged therefrom.

6. A method of propeller blade manufacture which comprises theprefabrication of channelshaped blade and spar elements, welding thesaid elements together to constitute a reenforced b-lade in which thereenforcing element provides a passage throughout the interior length ofthe blade, dislodging through said passage loose material left from thewelding, together with the steps of adhesively coating the interior ofsaid blade, and thereafter packing said blade with a material to fill atleast a portion thereof and to be adhesively positioned therein, wherebyto immobilize any further fragments remaining in said blade.

'7. A method of blade manufacture which comprises the construction ofchannel-shaped blade elements, each including a blade edge andcontiguous portions of its pressure and camber faces,V

said elements' having margins adapted for-edge t`o`- edge lconnectionupon said faces', thefabrication of separate'spar'sections adaptedto fitwithiny the respective elements andv tol extend longitudinally thereof,and the fastening together of the spar sections and the respectiveelements, including the'fusing of theA margins of said elements to eachother in butt engagement upon lines extending longitudinally of theopposingy faces of theblade and' along theline of connection betweenatleastone o the spar sections and one of said elements wherebyv thebutts of said elements are supported internally duringl thel fusingoperation by which they are connected, whereby to form an inter--Y nallyreenforced hollow blade. f

EMIL R'. LOCHMAN.

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